Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. A head that can read may be referred to as a “read head” herein, even if includes other structures and can perform other functions, such as a writer for writing, a heater for heating, a microactuator, etc.
In a modern magnetic hard disk drive device, each read head is a sub-component of a head-gimbal assembly (HGA) that typically includes a laminated flexure to carry the electrical signals to and from the read head. The HGA, in turn, is a sub-component of a head-stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flexible printed circuit (FPC). The plurality of HGAs is attached to various arms of the actuator.
Modern laminated flexures typically include flexure conductive traces that are isolated from a flexure structural layer by a flexure dielectric layer. So that the signals from/to the read head can reach the FPC on the actuator body, each HGA flexure includes a flexure tail that extends away from the read head along a corresponding actuator arm and ultimately attaches to the FPC adjacent the actuator body. That is, the flexure includes flexure traces that extend from adjacent the read head and continue along the flexure tail to flexure electrical connection points adjacent the FPC.
The FPC includes conductive electrical terminals that correspond to the electrical connection points of the flexure tail, and FPC conductive traces that lead from such terminals to a pre-amplifier chip. The FPC conductive traces are typically separated from an FPC stiffener by an FPC dielectric layer. The FPC may also include an FPC cover layer over the FPC conductive traces, the FPC cover layer having a window to allow electrical conduction to the pre-amplifier chip and access to the FPC terminals. To facilitate electrical connection of the flexure conductive traces to the FPC conductive electrical terminals during the HSA manufacturing process, the flexure tails must first be properly positioned relative to the FPC, so that the flexure conductive traces are aligned with the FPC conductive electrical terminals. Then the flexure tails must be held or constrained against the FPC conductive electrical terminals while the aforementioned electrical connections are made (e.g. by ultrasonic bonding, solder jet bonding, or solder bump reflow).
However, recently for some disk drive products, the aforementioned electrical connections may employ a type of anisotropic conductive film (ACF) bonding. An anisotropic conductive film is typically an adhesive doped with conductive beads or cylindrical particles of uniform or similar diameter. As the doped adhesive is compressed and cured, it is heated and squeezed between the surfaces to be bonded with sufficient uniform pressure that a single layer of the conductive beads makes contact with both surfaces to be bonded. In this way, the thickness of the adhesive layer between the bonded surfaces becomes approximately equal to the size of the conductive beads. The cured adhesive film may conduct electricity via the contacting beads in a direction normal to the bonded surfaces (though may not necessarily conduct electricity parallel to the bonded surfaces, since the beads may not touch each other laterally—though axially each bead is forced to contact both of the surfaces to be bonded—hence the term “anisotropic”).
Maintaining sufficiently uniform temperature and pressure during adhesive curing, such that a single layer of conductive beads in an ACF makes contact with both opposing surfaces to be bonded and curing is acceptably uniform, may be achievable in a high-volume manufacturing environment by pressing against several bond pads simultaneously with a thermode tool that applies acceptably uniform pressure and heat.
However, if the flexure tail includes one or more jumpers (e.g. to enable interleaving common traces for improved electrical characteristics), then a local thickness of the flexure tail at the location of such jumper(s) may interfere with the uniformity of applied pressure and heat from the thermode tool. For example, the jumper may receive an undesirable quantity of the heat and pressure applied by the thermode, potentially at the expense of the desired pressure and heat applied by the thermode to the bond pads.
Moreover, there is a risk that the pressure and heat undesirably applied to the jumper by the thermode tool may cause the jumper structure to undesirably short conductive traces of the abutting FPC, for example by disrupting the integrity of an overcoat layer. Hence, there is a need in the art for improved structures and methods to interconnect the flexure tails to the FPC in a disk drive, with improved uniformity of connection and/or reduced risk of incidental shorting, even where the presence of a jumper near the bond pads is desired.